Recuperator and combustor for use in external combustion engines and system for generating power employing same

ABSTRACT

A combustor/recuperator assembly for use in an external combustion engine, such as a Stirling engine. The assembly includes a plurality of substantially hemispherical domed members positioned in nested uniaxial spaced relation, the plurality of substantially hemispherical domed members forming at least a first flow chamber and a second flow chamber, the first flow chamber for passing an incoming charge of air therethrough and the second flow chamber for passing an outgoing charge of combustion exhaust gases therethrough, wherein the second chamber is positioned to be effective to heat the incoming charge of air. Also provided is a system for producing power from a source of liquid fuel. The system is capable of producing up to about 5,000 watts of mechanical or electrical power.

RELATED APPLICATIONS

This patent application claims priority from Provisional Application Ser. No. 60/484,508, filed on Jul. 1, 2003, the contents of which are hereby incorporated by reference.

FIELD

The present invention relates to external combustion engines. More particularly, the invention relates to an external combustion engine, such as a Stirling cycle engine, having a combustor/recuperator assembly design adapted to have improved heat transfer characteristics.

BACKGROUND

The Stirling cycle engine was originally conceived during the early portion of the nineteenth century by Robert Stirling. During the middle of the nineteenth century, commercial applications of this hot gas engine were devised to provide rotary power to mills. The Stirling engine was ignored thereafter until the middle of the twentieth century because of the success and popularity of the internal combustion engine. Stirling cycle machines, including engines and refrigerators, are described in detail in Walker, Stirling Engines, Oxford University Press (1980), incorporated herein by reference.

The principle underlying the Stirling cycle engine is the mechanical realization of the Stirling thermodynamic cycle: 1) isovolumetric heating of a gas within a cylinder, 2) isothermal expansion of the gas (during which work is performed by driving a piston), 3) isovolumetric cooling and 4) isothermal compression. Additional background regarding aspects of Stirling cycle machines and improvements thereto are discussed in Hargreaves, The Phillips Stirling Engine (Elsevier, Amsterdam, 1991), incorporated herein by reference.

The high theoretical efficiency of the Stirling engine has attracted considerable interest in recent years. The Stirling engine adds the additional advantages of easy control of combustion emissions, potential use of safer, cheaper, and more readily available fuels and quiet running operation, all of which combine to make the Stirling engine a highly desirable alternative to the internal combustion engine for many applications.

Despite these advantages, development of the Stirling engine has proceeded at a much slower rate than might otherwise be expected. Some of the more acute problems include the need to seal the working gas at a high pressure within the working space, the requirement for transferring heat at high temperature from the heat source to the working gas through the heater head, and a simple, reliable and inexpensive means for modulating the power as the load changes.

One design, which is well suited to a variety of applications, is the free-piston Stirling engine. The free-piston Stirling engine uses a displacer that is mechanically independent of the power output member. Its motion and phasing relative to the power output member is accomplished by the state of a balanced dynamic system of springs and masses, rather than a mechanical linkage.

Stirling engines have been proposed for use in a wide range of applications. Examples include automotive applications, refrigeration systems and applications in outer space. The need to power portable electronics equipment, communications gear, medical devices and other equipment in remote field service presents yet another opportunity, as these applications require power sources that provide both high power and energy density, while also requiring minimal size and weight, low emissions and cost.

To date, batteries have been the principal means for supplying portable sources of power. However, the time required for recharging batteries has proven inconvenient for continuous use applications. Moreover, portable batteries are generally limited to power production in the range of several milliwatts to a few watts and thus cannot address the need for significant levels of mobile, lightweight power production.

Small generators powered by internal combustion engines, whether gasoline- or diesel-fueled have also been used. However, the noise and emission characteristics of such generators have made them wholly unsuitable for a wide range of mobile power systems and unsafe for indoor use. While conventional heat engines powered by high energy density liquid fuels offer advantages with respect to size, thermodynamic scaling and cost considerations have tended to favor their use in larger power plants.

In view of these factors, a void exists with regard to power systems in the size range of approximately 50 to 500 watts. Moreover, in order to take advantage of high energy density liquid fuels, improved fuel preparation and delivery systems capable of low fueling rates are needed. Additionally, such systems must also enable highly efficient combustion with minimal emissions.

The drive to maximize engine efficiency has stimulated the introduction of several modifications to make the Stirling engine more suitable for a broader range of applications. The basic Stirling engine employs a continuous combustion system that can waste considerable energy via exhaust gases released to the atmosphere. For fixed use Stirling engines, heavy steel heat exchangers were devised to return a proportion of the exhaust heat energy to the inducted air to facilitate combustion. In automotive use, the heavy steel heat exchangers were replaced by rotary ceramic pre-heaters of the type, which earlier found utility in gas turbine engine applications. The rotary preheater functioned to expose hot gases through a crescent shaped opening to a rotating ceramic wheel, and separately exposed inducted air to the heated wheel at an independent crescent shaped opening. Small free-piston Stirling engines have provided their own unique challenges in the quest to improve engine efficiency, since inherent size restrictions limit the available options.

In view thereof and despite the advances in the art, there continues to be a need for a small free-piston Stirling engine having improved thermal efficiency characteristics.

SUMMARY

Provided is a combustor/recuperator assembly for use in an external combustion engine. The assembly includes a plurality of substantially hemispherical domed members positioned in nested uniaxial spaced relation, the plurality of substantially hemispherical domed members forming at least a first flow chamber and a second flow chamber, the first flow chamber for passing an incoming charge of air therethrough and the second flow chamber for passing an outgoing charge of combustion exhaust gases therethrough, wherein the second chamber is positioned to be effective to heat the incoming charge of air.

Also provided is a burner for an external combustion engine having a heater head. The burner includes a combustor/recuperator assembly for use in an external combustion engine having a heater head, the combustor/recuperator assembly including a plurality of substantially hemispherical domed members positioned in nested uniaxial spaced relation, the plurality of substantially hemispherical domed members forming at least a first flow chamber and a second flow chamber, the first flow chamber for passing an incoming charge of air therethrough and the second flow chamber for passing an outgoing charge of combustion exhaust gases therethrough, a fuel vaporizing device, the fuel vaporizing device including at least one capillary flow passage, the at least one capillary flow passage having an inlet end and an outlet end, the inlet end in fluid communication with a source of liquid fuel; and a heat source arranged along the at least one capillary flow passage, the heat source operable to heat the liquid fuel in the at least one capillary flow passage to a level sufficient to change at least a portion thereof from a liquid state to a vapor state and deliver a stream of substantially vaporized fuel from the outlet end of the at least one capillary flow passage and a combustion chamber defined by an inner surface of the combustor/recuperator assembly and an outer surface of the heater head of the external combustion engine, the combustion chamber having an igniter for combusting the stream of substantially vaporized fuel and air, the combustion chamber in communication with the outlet end of the at least one capillary flow passage, wherein the second chamber of the combustor/recuperator assembly is positioned to be effective to heat the incoming charge of air.

Also provided is a method of generating power. The method includes the steps of inducing a flow of air of through an intake system, supplying liquid fuel to at least one capillary flow passage, causing a stream of substantially vaporized fuel to pass through an outlet of the at least one capillary flow passage by heating the liquid fuel in the at least one capillary flow passage, combusting the air and vaporized fuel in a combustion chamber, exhausting a stream of combustion gases through an exhaust, exchanging heat from the stream of combustion gases exhausted to the flow of air induced for combustion through a recuperator; and converting heat produced by combustion of the vaporized fuel in the combustion chamber into mechanical and/or electrical power using an external combustion engine. The recuperator includes a plurality of substantially hemispherical domed members positioned in nested uniaxial relation, the plurality of substantially hemispherical domed members forming at least a first flow chamber and a second flow chamber, the first flow chamber for passing an incoming charge of air therethrough and the second flow chamber for passing an outgoing charge of combustion exhaust gases therethrough and the second chamber is positioned to be effective to heat the incoming charge of air.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described in more detail with reference to preferred forms of the invention, given only by way of example, and with reference to the accompanying drawings, in which:

FIG. 1 presents a schematic view of a fuel-vaporizing device, combustion chamber and exhaust heat recuperator;

FIG. 2 shows a perspective view of a combustor/recuperator assembly in cross-section, in accordance with an embodiment of the invention;

FIG. 3 presents a cross-sectional view of a combustor/recuperator assembly, in accordance with an embodiment of the invention;

FIG. 4 shows an enlarged cross-sectional view of a combustor/recuperator assembly, in accordance with an embodiment of the invention;

FIG. 5 presents a cross-sectional view of an alternate embodiment of a combustor/recuperator assembly, in accordance with the invention; and

FIG. 6 is a schematic view of an apparatus for generating power in accordance with the invention wherein an external combustion engine is used to generate electricity in accordance with one embodiment of the invention.

DETAILED DESCRIPTION

Reference is now made to the embodiments illustrated in FIGS. 1-6 wherein like numerals are used to designate like parts throughout.

The present invention provides a combustor/recuperator design suitable for use in external combustion engines, particularly Stirling engines. The design provides an arrangement of combustion air and exhaust flow passages, together with low-mass thermal insulation to ensure maximal transfer of high-quality heat to a load, such as an external combustion engine heater head and efficient transfer of low-quality heat in the recuperator to preheat the combustion air. This results in the transfer of heat to the load with maximum efficiency in a compact, lightweight and cost-effective design.

As is well known, the Stirling engine is an external combustion engine, employing an external continuous combustion system for heating. Generally, this continuous combustion system is comprised of an induction system, an exhaust and a combustion chamber. To enhance overall system efficiency, it is advantageous to employ a means of preheating the inducted air stream.

The burning of fuel to supply heat to the heater head is constrained in many ways. For example, heat must be supplied at between approximately 500° C. and 750° C. The surface area available on the heater head requires that either very high heat flux rates must be generated from the combustion heat source or an extended heater head surface must be provided, or both. Moreover, it is important that heat transfer and head temperature should be as uniform as possible and combustion should be accomplished with the minimum generation of pollutant species, such as NO_(x), CO, and unburned hydrocarbons.

To maximize the conversion efficiency of the system, highly preheated combustion air should be used. To accomplish this, the air is preheated in a recuperator. However, the high combustion air temperature significantly increases the potential for forming NO_(x) emissions from the combustor. The combustor should be operated at as low a level of excess air as possible, to minimize stack losses and maximize system efficiency. For maximum combustor efficiency, high-quality heat, that is the heat directly available from combustion, should be transferred directly to the engine heater head, while the lower quality heat, that is the heat of the exhaust stream, should be used to preheat the combustion air in the recuperator.

Referring now to FIG. 1, a schematic view of a Stirling engine combustor/recuperator section 10 is shown. Fuel and air enter the combustion chamber 12 at a common temperature, which is ambient temperature, T₀. Combustion products leave at a common uniform temperature, T₄.

The temperature at which combustion products make final contact with the outer surface of the expansion exchanger 14 must be above the nominal source temperature, T_(E). As may be appreciated, to exhaust the combustion products at this temperature would remove any possibility of achieving high overall efficiency, so the combustion system should provide for air pre-heating by the exchange of heat with the exhaust. Still referring to FIG. 1, air enters the inlet 16 of pre-heating passage 18 of recuperator 20 at T₀ emerging at outlet 24 a temperature T_(b) after gaining heat from the exhaust via the recuperator 20.

Fuel is introduced at outlet 26 of fuel delivery device 28 at a temperature T₀. Optionally, it may be injected by entrainment with a source of high-pressure air 30 at a rate of m′_(ap). As may be appreciated, the net air/fuel ratio for such a system is based on the sum of both air streams, m′_(a)=(m′_(ap)+m′_(as)). With modest pre-heating, fuel and air may be premixed. A particularly preferred capillary-based fuel-vaporizing device for use in the practice of the present invention is disclosed in U.S. application Ser. No. 10/143,463, the contents of which are hereby incorporated in their entirety.

Thereafter, combustion takes place in combustion chamber 12, yielding temperature T₂. Combustion for this example is taken to be complete before the products pass over the expansion exchanger 14, where they exit at T₃. This is the temperature at which the products enter the exhaust inlet 32 of exhaust passage 22 of recuperator 20. The exhaust products leave at T₄ after exchanging heat with incoming air.

Referring now to FIGS. 2-4, the present invention seeks to efficiently transfer heat to the heater head of a Stirling engine with maximum efficiency in a compact, lightweight and cost-effective design. As shown, the combustor housing/recuperator assembly is formed from a nested set of four substantially hemispherical domes. The four domes include an intake dome 150, which may be fabricated from stainless steel or one of the well-known super alloys having a wall thickness of from about 0.5 to about 1 mm, a recuperator dome 152, which may also be fabricated from stainless steel having a wall thickness of from about 0.5 to about 1 mm, an exhaust dome 154, which again may be fabricated from stainless steel having a wall thickness of about 1 mm, and an inner dome 156, which again may be fabricated from stainless having a wall thickness of about 1 mm. Refractory material 160 is affixed to inner dome 156 to further insulate intake dome 150, recuperator dome 152 and exhaust dome 154 from the heat of combustion and enhance the ability to transfer the highest amount of heat to the outer surface of Stirling engine heater head 170 (see FIG. 3). To further aid in the transfer of heat, heater head 170, which may be constructed from stainless steel, can be further clad with a layer of copper. As shown in FIG. 4, nested stainless steel domes are set in a spaced relation to form the passages discussed below. The stainless steel domes may be joined by welds or brazing, with a full round or half-tube welded to the ceramic shell to position same.

Referring to FIGS. 2 and 4, combustion air is introduced into an inlet 180 and into upper manifold 182, where it flows down through a plurality of manifold runners 184, through an outer shell passage 186 formed by the combination of the intake dome 150 and recuperator dome 152. The combustion air then picks up heat by convective heat transfer from the exiting combustion products flowing through exhaust shell passage 190 formed by the combination of the exhaust dome 154 and the inner dome 156. The air is passes through a plurality of circumferentially arranged slots 194 and is re-directed upwards through an inner shell passage 192, formed by the combination of the recuperator dome 152 and the exhaust dome 154, and heats further, finally passing via the upper manifold 182 into the central combustion zone 200, where it is mixed with fuel and is ignited. The combustor can be operated in either diffusion flame mode, by introducing fuel along the central axis through the manifold 182, or in a premixed mode, by introducing fuel into the recuperator passages or the manifold 182. The combustion zone heats the Stirling engine heater head 170 by a mixture of convection and radiation. The combustion products exit at the bottom of the heater head and flow upwards through the exhaust shell passage 190 formed by the combination of the exhaust dome 154 and the inner dome 156, which is located behind lightweight refractory insulation 160.

Preferred refractory materials include lightweight, high-purity, alumina-silica fiber, having a duty rating of at least about 2300° F., with a more preferred range of duty ratings of at least about 2600 to about 2800° F. Such materials have characteristically low thermal conductivity, low specific heat, high thermal-shock resistance and very good durability. The refractory materials appropriate for use in the present invention possess an approximate thermal conductivity (ASTM C-201) value of at least about 0.8 BTU In/Hr/Ft² at a mean temperature of 1000° F. A source for such materials is Refractory Specialties Incorporated, of Sebring, Ohio, which markets them under the Gemcolite™ brand.

As may be appreciated by those skilled in the art, the location of the insulation adjacent to the flame zone increases efficiency by not allowing the high quality heat to be transferred via the cold recuperator walls to the incoming air and the outside environment.

As is preferred, the combustor may be fueled using a source of gaseous fuel or may be fitted with a fuel system capable of providing a vaporized high energy density liquid fuel for combustion. Suitable fuels that exist as gases at standard temperatures and pressures (ambient conditions) include such hydrocarbon fuels as methane, ethane, propane and butane.

Alternatively, a fuel vaporizer suitable for use in the present invention is shown schematically in FIG. 3. Referring now to FIG. 3, the combustor/recuperator assembly of the present invention may be fitted with a fuel vaporizer, which may include at least one capillary sized flow passage 300 for connection to a fuel supply (not shown). As disclosed in U.S. application Ser. No. 10/143,463, a heat source is arranged along the flow passage 300 to heat liquid fuel in the flow passage sufficiently to deliver a stream of vaporized fuel from an outlet of the flow passage into the combustion zone 200, wherein the vaporized fuel is combusted. The flow passage 300 can be a capillary tube heated by a resistance heater, a section of the tube heated by passing electrical current therethrough. As is particularly preferred, the capillary flow passage should have a low thermal inertia, so that capillary passage 300 can be brought up to the desired temperature for vaporizing fuel very quickly, e.g., within 2.0 seconds, preferably within 0.5 second, and more preferably within 0.1 second. The capillary sized fluid passage is preferably formed in a capillary body such as a single or multilayer metal, ceramic or glass body. The passage has an enclosed volume opening to an inlet and an outlet either of which may be open to the exterior of the capillary body or may be connected to another passage within the same body or another body or to fittings. The heater can be formed by a portion of the body such as a section of a stainless steel tube or the heater can be a discrete layer or wire of resistance heating material incorporated in or on the capillary body.

FIG. 5 presents a cross-sectional view of an alternate embodiment of a combustor/recuperator assembly, in accordance with another aspect of the invention. The combustor housing/recuperator assembly is formed from a nested set of four substantially hemispherical domes, although the outer three domes are flared-out, as shown, to accommodate manifolding. The four domes include an intake dome 550, which may be fabricated from stainless steel having a wall thickness of from about 0.5 to about 1 mm, a recuperator dome 552, which may also be fabricated from stainless steel having a wall thickness of from about 0.5 to about 1 mm, an exhaust dome 554, which again may be fabricated from stainless steel having a wall thickness of about 1 mm, and an inner dome 556, which again may be fabricated from stainless steel having a wall thickness of about 1 mm. Refractory material 560 is affixed to inner dome 556 to further insulate intake dome 550, recuperator dome 552 and exhaust dome 554 from the heat of combustion and enhance the ability to transfer the highest amount of heat to the outer surface of a Stirling engine heater head (not shown). As shown, nested stainless steel domes are set in a spaced relation to form intake and exhaust passages. The stainless steel domes may be joined by welds or braising.

Advantageously, inner dome 560 may be spring loaded against exhaust dome 554, rather than rigidly fixed thereto, to provide flexibility during the heating of the assembly and thermal growth of exhaust dome 554. This also prevents the grinding away over time of the inner dome 560, which results from vibratory motion of the Stirling engine. Another suitable arrangement includes the use of a ceramic/metal felt of the type employed in gas turbine engines, as those skilled in the art will recognize.

In operation, combustion air is introduced into an inlet 580, where it flows down through outer shell passage 586 formed by the combination of the intake dome 550 and recuperator dome 552. The combustion air then picks up heat by convective heat transfer from the exiting combustion products flowing through exhaust shell passage 590 formed by the combination of the exhaust dome 554 and the inner dome 556. The air passes through a plurality of circumferentially arranged slots 594 and is re-directed upwards through an inner shell passage 592, formed by the combination of the recuperator dome 552 and the exhaust dome 554, and heats further, finally passing via the upper manifold 582, through a plurality of exit slots 588 into the central combustion zone 600, where it is mixed with fuel and is ignited. As may be appreciated, the combustion air passing though the plurality of exit slots 588 serves to impart a swirling motion to the combustion air. The swirling air serves to create a more homogenous mixture of air and fuel for combustion, producing a more stable flame. The combustion zone heats the Stirling engine heater head (not shown) by a mixture of convection and radiation. The combustion products exit at the bottom of the heater head and flow upwards through the exhaust shell passage 590 formed by the combination of the exhaust dome 554 and the inner dome 556, which is located behind lightweight refractory insulation 560.

Once again, preferred refractory materials include lightweight, high-purity, alumina-silica fiber, having a duty rating of at least about 2300° F., with a more preferred range of duty ratings of at least about 2600 to about 2800° F. The refractory materials appropriate for use in the present invention possess an approximate thermal conductivity (ASTM C-201) value of at least about 0.8 BTU In/Hr/Ft² at a mean temperature of 1000° F. A source for such materials is Refractory Specialties Incorporated, of Sebring, Ohio, which markets them under the Gemcolite™ brand.

As with the embodiment of FIGS. 2-4, the location of the insulation adjacent to the flame zone increases efficiency by not allowing the high quality heat to be transferred via the cold recuperator walls to the incoming air and the outside environment.

FIG. 6 shows a schematic of a power system 400 in accordance with another aspect of the present invention. Power system 400 includes an external combustion engine 430, such as a kinematic Stirling engine or a free-piston Stirling engine, a combustion chamber 434 wherein heat at 550-750° C. is converted into mechanical power by a reciprocating piston which drives an alternator 432 to produce electrical power. The assembly also includes a capillary flow passage/heater assembly 436, a controller 438, a rectifier/regulator 440, a battery 442, a fuel supply 444, a combustor/recuperator assembly 446, of the type disclosed above and depicted in FIGS. 2-4, a combustion blower 448, a cooler 450 and a cooler/blower 452. In operation, the controller 438 is operable to control delivery of fuel to the capillary 436 and to control combustion of the fuel in the chamber 434 such that the heat of combustion drives a piston in the Stirling engine 430 such that the engine outputs electricity from the alternator 432. If desired, the Stirling engine 430/alternator 432 can be replaced with a kinematic Stirling engine (not shown) which outputs mechanical power.

In order to initiate combustion, the air-fuel mixture can be confined in an ignition zone in which an igniter such as a spark generator ignites the mixture. The igniter can be any device capable of igniting the fuel such as a mechanical spark generator, an electrical spark generator, resistance heated ignition wire or the like. The electrical spark generator can be powered by any suitable power source, such as a small battery. However, the battery can be replaced with a manually operated piezoelectric transducer that generates an electric current when activated. With such an arrangement, current can be generated electro-mechanically due to compression of the transducer. For instance, a striker can be arranged so as to strike the transducer with a predetermined force when the trigger is depressed. The electricity generated by the transducer can be supplied to a spark generating mechanism by suitable circuitry. Such an arrangement could be used to ignite the fuel-air mixture.

Some of the electrical power generated can be stored in a suitable storage device such as a battery or capacitor, which can be used to power the igniter. For example, a manually operated switch can be used to deliver electrical current to a resistance-heating element or directly through a portion of a metal tube, which vaporizes fuel in the flow passage and/or the electrical current can be supplied to an igniter for initiating combustion of the fuel-air mixture delivered to the combustion chamber.

If desired, the output of the power system could be used to operate any type of device that relies on mechanical or electrical power. For instance, electricity generated could be used for portable electrical equipment such as telephone communication devices (e.g., wireless phones), portable computers, power tools, appliances, camping equipment, military equipment, transportation equipment such as mopeds, powered wheelchairs and marine propulsion devices, electronic sensing devices, electronic monitoring equipment, battery chargers, lighting equipment, heating equipment, etc. The power system could also be used to supply power to non-portable devices or to locations where access to an electrical power grid is not available, inconvenient or unreliable. Such locations and/or non-portable devices include remote living quarters and military encampments, vending machines, marine equipment, etc.

While the invention has been described in detail with reference to preferred embodiments thereof, it will be apparent to one skilled in the art that various changes can be made, and equivalents employed, without departing from the scope of the invention. 

1. A combustor/recuperator assembly for use in an external combustion engine having a heater head, comprising: a plurality of substantially hemispherical domed members positioned in nested uniaxial spaced relation, said plurality of substantially hemispherical domed members forming at least a first flow chamber and a second flow chamber, said first flow chamber for passing an incoming charge of air therethrough and said second flow chamber for passing an outgoing charge of combustion exhaust gases therethrough, wherein said second chamber is positioned to be effective to heat the incoming charge of air.
 2. The assembly of claim 1, wherein said plurality of substantially hemispherical domed members comprises: (a) an intake dome having an outer surface and an inner surface; (b) a recuperator dome having an outer surface and an inner surface; (c) an exhaust dome having an outer surface and an inner surface; and (d) an inner dome having an outer surface and an inner surface, wherein said recuperator dome is positioned between said inner surface of said intake dome and said outer surface of said exhaust dome and said outer surface of said inner dome is adjacent said inner surface said exhaust dome.
 3. The assembly of claim 2, further comprising refractory material affixed to said inner surface of said inner dome to insulate said intake dome, said recuperator dome and said exhaust dome from heat produced by combustion, whereby said refractory material enhances the ability to transfer heat to the outer surface of the external combustion engine heater head.
 4. The assembly of claim 3, wherein said refractory material is a lightweight, high-purity, alumina-silica fiber, having a duty rating of at least about 2300° F.
 5. The assembly of claim 4, wherein said refractory material has an approximate thermal conductivity value of at least about 0.8 BTU In/Hr/Ft² at a mean temperature of 1000° F.
 6. The assembly of claim 4, wherein the heater head of the external combustion engine is clad with a layer of copper to enhance heat transfer to the heater head.
 7. The assembly of claim 1, wherein the heater head of the external combustion engine is clad with a layer of copper to enhance heat transfer to the heater head.
 8. The assembly of claim 2, wherein said intake dome is fabricated from stainless steel having a wall thickness of from about 0.5 to about 1 mm.
 9. The assembly of claim 2, wherein said recuperator dome is fabricated from stainless steel having a wall thickness of from about 0.5 to about 1 mm.
 10. The assembly of claim 2, wherein said exhaust dome is fabricated from stainless steel having a wall thickness of about 1 mm.
 11. The assembly of claim 2, wherein said inner dome has a wall thickness of about 1 mm.
 12. A burner for an external combustion engine having a heater head, comprising: (a) combustor/recuperator assembly for use in the external combustion engine having a heater head, said combustor/recuperator assembly including a plurality of substantially hemispherical domed members positioned in nested uniaxial spaced relation, said plurality of substantially hemispherical domed members forming at least a first flow chamber and a second flow chamber, said first flow chamber for passing an incoming charge of air therethrough and said second flow chamber for passing an outgoing charge of combustion exhaust gases therethrough; (b) a fuel vaporizing device, said fuel vaporizing device including at least one capillary flow passage, said at least one capillary flow passage having an inlet end and an outlet end, said inlet end in fluid communication with a source of liquid fuel; and a heat source arranged along said at least one capillary flow passage, said heat source operable to heat the liquid fuel in said at least one capillary flow passage to a level sufficient to change at least a portion thereof from a liquid state to a vapor state and deliver a stream of substantially vaporized fuel from said outlet end of said at least one capillary flow passage; and (d) a combustion chamber defined by an inner surface of said combustor/recuperator assembly and an outer surface of the heater head of the external combustion engine, said combustion chamber having an igniter for combusting the stream of substantially vaporized fuel and air, said combustion chamber in communication with said outlet end of said at least one capillary flow passage, wherein said second chamber of said combustor/recuperator assembly is positioned to be effective to heat the incoming charge of air.
 13. The burner of claim 12, wherein said plurality of substantially hemispherical domed members comprises: (a) an intake dome having an outer surface and an inner surface; (b) a recuperator dome having an outer surface and an inner surface; (c) an exhaust dome having an outer surface and an inner surface; and (d) an inner dome having an outer surface and an inner surface, wherein said recuperator dome is positioned between said inner surface of said intake dome and said outer surface of said exhaust dome and said outer surface of said inner dome is adjacent said inner surface said exhaust dome.
 14. The burner of claim 13, further comprising refractory material affixed to said inner surface of said inner dome to insulate said intake dome, said recuperator dome and said exhaust dome from heat produced by combustion, whereby said refractory material enhances the ability to transfer heat to the outer surface of the external combustion engine heater head.
 15. The burner of claim 14, wherein said refractory material is a lightweight, high-purity, alumina-silica fiber, having a duty rating of at least about 2300° F.
 16. The burner of claim 15, wherein said refractory material has an approximate thermal conductivity value of at least about 0.8 BTU In/Hr/Ft² at a mean temperature of 1000° F.
 17. The burner of claim 15, wherein the heater head of the external combustion engine is clad with a layer of copper to enhance heat transfer to the heater head.
 18. The burner of claim 12, wherein the heater head of the external combustion engine is clad with a layer of copper to enhance heat transfer to the heater head.
 19. The burner of claim 13, wherein said intake dome is fabricated from stainless steel having a wall thickness of from about 0.5 to about 1 mm.
 20. The burner of claim 13, wherein said recuperator dome is fabricated from stainless steel having a wall thickness of from about 0.5 to about 1 mm.
 21. The burner of claim 13, wherein said exhaust dome is fabricated from stainless steel having a wall thickness of about 1 mm.
 22. The burner of claim 13, wherein said inner dome has a wall thickness of about 1 mm.
 23. The burner of claim 12, wherein said heat source comprises a resistance-heating element.
 24. The burner of claim 23, wherein said at least one capillary flow passage comprises at least one capillary tube.
 25. The burner of claim 24, wherein said heat source comprises a section of said capillary tube heated by passing an electrical current therethrough.
 26. The burner of claim 12, further comprising a fuel source, said fuel source capable of delivering pressurized liquid fuel to said at least one capillary flow passage at a pressure of 100 psig or less.
 27. A method of generating power, comprising; (a) inducing a flow of air of through an intake; (b) supplying liquid fuel to at least one capillary flow passage; (c) causing a stream of substantially vaporized fuel to pass through an outlet of the at least one capillary flow passage by heating the liquid fuel in the at least one capillary flow passage; (d) combusting the air and vaporized fuel in a combustion chamber; (e) exhausting a stream of combustion gases through an exhaust; (f) exchanging heat from the stream of combustion gases exhausted in step (e) to the flow of air induced in step (a) through a recuperator; and (g) converting heat produced by combustion of the vaporized fuel in the combustion chamber into mechanical and/or electrical power using an external combustion engine, wherein the recuperator includes a plurality of substantially hemispherical domed members positioned in nested uniaxial relation, the plurality of substantially hemispherical domed members forming at least a first flow chamber and a second flow chamber, the first flow chamber for passing an incoming charge of air therethrough and the second flow chamber for passing an outgoing charge of combustion exhaust gases therethrough and the second chamber is positioned to be effective to heat the incoming charge of air.
 28. The method of claim 27, wherein the at least one capillary flow passage includes at least one capillary tube and the heat source comprises a resistance heating element or section of the capillary tube heated by passing an electrical current therethrough, the method further including flowing the liquid fuel through the capillary tube and vaporizing the liquid fuel by heating the tube.
 29. The method of claim 27, wherein the combustion chamber includes an igniter arranged to ignite the vaporized fuel, the method including igniting the vaporized fuel with the igniter.
 30. The method of claim 27, wherein the external combustion engine outputs up to 5000 watts of mechanical or electrical power, the method including generating power at one or more points in a range of up to 5000 watts of power with the conversion device.
 31. The method of claim 27, wherein the plurality of substantially hemispherical domed members comprises: (a) an intake dome having an outer surface and an inner surface; (b) a recuperator dome having an outer surface and an inner surface; (c) an exhaust dome having an outer surface and an inner surface; and (d) an inner dome having an outer surface and an inner surface, wherein the recuperator dome is positioned between the inner surface of the intake dome and the outer surface of the exhaust dome and the outer surface of the inner dome is adjacent the inner surface the exhaust dome.
 32. The method of claim 31, further comprising refractory material affixed to the inner surface of the inner dome to insulate the intake dome, the recuperator dome and the exhaust dome from heat produced by combustion, whereby the refractory material enhances the ability to transfer heat to the outer surface of the external combustion engine heater head.
 33. The method of claim 32, wherein the refractory material is a lightweight, high-purity, alumina-silica fiber, having a duty rating of at least about 2300° F.
 34. The method of claim 33, wherein the refractory material has an approximate thermal conductivity value of at least about 0.8 BTU In/Hr/Ft² at a mean temperature of 1000° F.
 35. The method of claim 33, wherein the heater head of the external combustion engine is clad with a layer of copper to enhance heat transfer to the heater head.
 36. The method of claim 27, wherein the heater head of the external combustion engine is clad with a layer of copper to enhance heat transfer to the heater head.
 37. The method of claim 28, wherein the intake dome is fabricated from stainless steel having a wall thickness of from about 0.5 to about 1 mm.
 38. The method of claim 28, wherein the recuperator dome is fabricated from stainless steel having a wall thickness of from about 0.5 to about 1 mm.
 39. The method of claim 28, wherein the exhaust dome is fabricated from stainless steel having a wall thickness of about 1 mm.
 40. The method of claim 28, wherein the inner dome has a wall thickness of about 1 mm. 